The renin-angiotensin system (RAS) plays a central role in the regulation of normal blood pressure and seems to be critically involved in hypertension development and maintenance as well as in congestive heart failure. Angiotensin II (A II), is an octapeptide hormone produced mainly in the blood during the cleavage of angiotensin I by angiotensin converting enzyme (ACE) localized on the endothelium of blood vessels of lung, kidney, and many other organs. It is the end product of the renin-angiotensin system (RAS) and is a powerful arterial vasoconstrictor that exerts its action by interacting with specific receptors present on cell membranes. One of the possible modes of controlling the RAS is angiotensin II receptor antagonism. Several peptide analogs of angoitensin II (A II) are known to inhibit the effect of this hormone by competitively blocking the receptors, but their experimental and clinical applications have been limited by partial agonist activity and lack of oral absorption [M. Antonaccio. Clin. Exp. Hypertens. A4, 27-46 (1982); D. H. P. Streeten and G. H. Anderson, Jr., Handbook of Hypertension, Clinical Pharmacology of Antihypertensive Drugs, ed. A. E. Doyle, Vol. 5, pp. 246-271, Elsevier Science Publisher, Amsterdam, The Netherlands, 1984].
Recently, several non-peptide compounds have been described as A II antagonists. Illustrative of such compounds are those disclosed in U.S. Pat. Nos. 4,207,324; 4,340,598; 4,576,958; and 4,582,847; and 4,880,804 in European Patent Application Nos. 028,834; 245,637; 253,310; 323,841; and 291,969; and in articles by A. T. Chiu, et al. [Eur. J. Pharm. Exp. Therap, 157, 13-21 (1988)] and by P. C. Wong, et al. [J. Pharm. Exp. Therap, 247, 1-7(1988)]. All of the cited references disclose compounds containing substituted imidazole and triazole compounds, which are generally bonded through a lower alkyl bridge to a substituted phenyl and preferably a biphenyl moiety containing a carboxylic acid or an acid equivalent. European Patent Application No. 245,637 discloses derivatives of 4,5,6,7-tetrahydro-2H-imidazol-[4,5-c]pyridine-6-carboxylic acid and analogs thereof as antihypertensive agents.
The process previously used in the synthesis of 1-(tetrazol-5-yl)-2-(4-tolyl)benzene entailed the cross-coupling of p-tolylzinc chloride and 1-cyano-2-bromobenzene, the biphenyl adduct is then converted to the tetrazole with ammonium azide (Finnegan, et al., J. Am. Chem. Soc., 80, 3908-11, 1958.) or trimethyltin azide (Aldrich, et al., U.S. Pat. No. 4,870,186) to give the product 1-(tetrazol-5-yl)-2-(4-tolyl)benzene. The ammonium azide procedure requires long reaction times and produces low yields of the desired material. Prior to this invention, the preferred procedure required the use of trimethylstannyl chloride to generate the trimethylstannyl azide followed by reaction with the biphenyl adduct to give the desired tetrazole and the corresponding tin by-products. The disposal of these by-products is costly and coupled with the toxicity of tin make this route commercially unattractive.
These problems can be circumvented by the present invention which employs the reverse sequence of steps. The ortho-lithiation procedure is performed on (tetrazol-5-yl)benzene which is readily available from benzonitrile and ammonium azide (Finnegan, et. al.), or its N-trityl protected derivative, in high yields. The novel ortho-lithiation procedure allows for the preparation of the desired 1-(tetrazol-5-yl)-2-(4-tolyl)benzene through a more versatile and cost effective method.